The last time the Strawbs played Ann Arbor, in 2008, it was as a five-piece electric band.

That was a special occasion — a tour that reunited the group’s 1974-’75 lineup — the one that recorded the group’s best-known progressive-rock albums, “Hero & Heroine” and “Ghosts.” Those were the records that got them the most attention in the U.S. in the mid-‘70s, with both making impressive showings on the Billboard Top 100 charts

This time, however, when they come to The Ark on Thursday, they will be performing as the Acoustic Strawbs trio.

Indeed, of the Strawbs’ 150 shows a year, about 2/3 of them feature the acoustic trio line-up, says Dave Cousins, the band’s leader, singer and main songwriter. That’s especially true when the English group comes to the U.S. or Canada.

That’s partly due to economics — it’s just too costly for a British act to lug a five-man band, with a drum kit, across the ocean and then drag them around “the colonies.” But the Acoustic Stawbs are not lacking when it comes to the fullness of their sound.

Even though the trio lineup features just Cousins and Dave Lambert on acoustic guitars, and Chas Cronk on bass, it doesn’t sound “stripped down.”

That’s primarily because of the unique tunings and chordings they employ.

“When we play songs as the acoustic trio that were recorded on one of our more produced, full-band albums, it definitely requires a rethinking of the songs,” says Cousins by phone from his home in England, near Brighton. “And it’s actually fun to work them out.

For starters, Cousins has always been a fan of alternate guitar tunings — “ones that are different the tunings the other guys are using, and we often use a 12-string. So, since we’re using three different tunings, and different chord inversions, it actually sounds more like nine guitars, not three. Plus Chas uses the foot pedals, so using that whole approach really does multiply the sound by a factor of about three.”

You can hear that full, ringing sound on the group’s 2009 DVD, “Live at Hampton Court Palace.” At that event, they were invited by Rick Wakeman (who did a stint in the Strawbs way back in the group’s early days, before he hooked up with Yes), to open for him. Wakeman was doing a full-on production of his “The Six Wives of Henry the VIII” composition, accompanied by his band, plus The English Chamber Choir and The Orchestra Europa.

Hampton Court is a historic and visually stunning palace, so the group could not have asked for a more grand-looking façade to be used as a backdrop for their performance. The set included their inventively-acoustic re-workings of Strawbs faves, like “Lay Down,” “New World,” “Shine On Silver Sun,” “Ghosts” and “A Glimpse of Heaven.”

The DVD also offers four audio-only bonus tracks, for which the Acoustic Strawbs briefly became a quartet, when Wakeman joined them on piano on “Witchwood,” “Oh How She Changed” “We’ll Meet Again Sometime” and a further re-worked “alternate version” of “A Glimpse of Heaven.

Although the Strawbs were / are better known in the U.S. as a more of a prog rock ensemble, they actually first earned their reputation in England, starting in the late ‘60s, as a folk-rock band. Early incarnations of the group included not only Wakeman, but also Sandy Denny, who later went on to join Fairport Convention.

The Strawbs also released a full-band CD in ’09, “Dancing to the Devil’s Beat,” for which they recruited Wakeman’s son, Oliver, to play keyboards and handle orchestrations. It was a progressive-folk-rock affair, with some songs leaning in the knottier prog-rock direction, and some capturing a more bucolic Brit-folk sound. Listen to a clip of Strawbs "Revenge (Can Be So Sweet) from "Dancing to the Devil’s Beat," (MP3).

Many of the songs conveyed angry sentiments about the state of the world, though.

“When I wrote those songs (in 2008) I was angry about the political situations in the U.S. and England, and about climate change, and the banking-system mess, and the wars in Iraq and Afghanistan,” recalls Cousins. “And we had recently visited the graves of the war dead in northern France. I just had the sense that everything was going wrong, and I felt compelled to make these political statements and commentaries.

“Angry Sky,” for example, takes on climate change, and those who deny its existence, and the “Pro Partia Suite” indirectly tackles the wars in Iraq and Afghanistan, “and is, in one way, about soldiers who die not knowing what cause they’re actually fighting for.”

Cousins and his mates have been hard at work on a couple of new projects, which are slated for release this month. One is a double CD that documents the Strawbs' 40th Anniversary Concerts last September, and the other is a CD / DVD that captures a duet concert Cousins did with Wakeman late last year.

Plus, Cousins has put together a book, “Secrets, Stories and Songs,” in which he tells the stories that inspired the 200-plus songs he has written over the years. The book includes a spoken-word CD, with Cousins reading the lyrics of almost 20 of the songs. And, the book reveals some of the odd tunings he has used over the years. “So, people who want to learn how to play our songs can finally figure them out,” he says with a laugh.

The 40th anniversary show was an emotional event, recalls Cousins. “It featured three different Strawbs line-ups, including Rick, and Oliver, and there were probably 50 musicians in all who were part of those shows. Having everyone there, for that weekend, just struck me, more than ever had before, what an incredibly talented array of musicians have passed through this band over the years.”

Kevin Ransom, a free-lance writer who covers music for AnnArbor.com, previously wrote about the Strawbs for the Ann Arbor News in 2008. He can be reached at KevinRansom10@aol.com.

Watch a promo video for the Strawbs 40th anniversary DVD: